Polysilane compositions, methods for their synthesis and films formed therefrom

ABSTRACT

Polysilanes, inks containing the same, and methods for their preparation are disclosed. The polysilane generally has the formula H—[(AHR) n (c—A m H pm−2 ) q ]—H, where each instance of A is independently Si or Ge; R is H, —A a H a+1 R a , Halogen, aryl or substituted aryl; (n+a)≧10 if q=0, q≧3 if n=0, and (n+q)≧6 if both n and q≠0; p is 1 or 2; and m is from 3 to 12. In one aspect, the method generally includes the steps of combining a silane compound of the formula AH a R 1   4−a , the formula A k H g R 1′   h  and/or the formula c—A m H pm R 1   rm  with a catalyst of the formula R 4   x R 5   y MX z  (or an immobilized derivative thereof) to form a poly(aryl)silane; then washing the poly(aryl)silane with an aqueous washing composition and contacting the poly(aryl)silane with an adsorbent to remove the metal M. In another aspect, the method includes the steps of halogenating a polyarylsilane to form a halopolysilane; and reducing the halopolysilane with a metal hydride to form the polysilane. The synthesis of semiconductor inks via dehydrocoupling of silanes and/or germanes allows for tuning of the ink properties (e.g., viscosity, boiling point, and surface tension) and for deposition of silicon films or islands by spincoating, inkjetting, dropcasting, etc., with or without the use of UV irradiation.

RELATED APPLICATIONS

This application is a divisional of Ser. No. 11/246,014 now U.S. Pat. No. 7,485,691, filed Oct. 6, 2005, and claims the benefit of U.S. Provisional Application No. 60/617,562, filed Oct. 8, 2004, which are incorporated herein by reference in their entirety.

FIELD OF THE INVENTION

The present invention generally relates to the field of polysilanes and methods of making the same. More specifically, embodiments of the present invention pertain to polysilane compounds, compositions and methods for making and using the same.

SUMMARY OF THE INVENTION

Embodiments of the present invention relate to polysilanes, polysilane ink compositions, methods for making the same and methods of making a semiconducting film using the same. The compounds generally comprise a polysilane of the formula H—[(AHR)_(n)—(c—A_(m)H_(pm−2)R′_(rm))_(q)]—H, where each instance of A is independently Si or Ge; each instance of R and R′ is independently H, —A_(b)H_(b+1)R² _(b) (where R² is H, aryl or substituted aryl), halogen, aryl or substituted aryl, but if q=0 and A is Si, R is not phenyl; (n+b)≧10 if q=0, q≧3 if n=0, and (n+q)≧6 if both n and q≠0; p is 1 or 2; (p+r)=2; and each instance of m is independently from 3 to 12. In general, n, b and/or q*m may be the number of silicon and/or germanium atoms in the polysilane according to the number average molecular weight (Mn) of the polysilane. The compositions generally comprise the polysilane compound (particularly the polysilanes in which R═H or —A_(a)H_(2a+1)) and a solvent in which the polysilane is soluble.

One method of making a polysilane generally comprises the steps of (a) combining a silane compound of the formula AH_(a)R¹ _(4−a), the formula A_(k)H_(g)R^(1′) _(h) and/or the formula c—A_(m)H_(pm)R^(1′) _(rm) with a catalyst of the formula R⁴ _(x)R⁵ _(y)MX_(z) (or an immobilized derivative thereof or which may be synthesized in situ from the corresponding precursors) to form a poly(aryl)silane of the formula H—[(AHR¹)_(n)—(c—A_(m)H_((pm−2))R^(1′) _(rm))_(q)]—H, where each instance of A is independently Si or Ge, a=2 or 3, and each instance of R¹ is independently aryl, substituted aryl, or —A_(b)H_(b+1)R² _(b) (where R² is aryl or substituted aryl); (n+b)≧10 if q=0, q≧3 if n=0, and (n+q)≧6 if both n and q≠0; k is an integer from 2 to 12, g≧2 and (g+h)=2k+2; p is 1 or 2, m is an integer from 3 to 12, p is 1 or 2, and r is 0 or 1; R^(1′) is the same as R¹, except that when R¹ is —A_(b)H_(b+1)R² _(b) or the silane compound of the formula AH_(a)R¹ _(4−a) is substantially absent, R^(1′) may be H; M is a metal selected from the group consisting of Ti, Zr and Hf, x=1 or 2, y=1, 2 or 3, z=0, 1 or 2, 3≦(x+y+z)≦8, each of the x instances of R⁴ is independently a substituted or non-substituted cyclopentadienyl, indenyl, fluorenyl, siloxyl, germoxyl, hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, or hydrocarbylsulfido ligand; each of the y instances of R⁵ is independently a substituted or non-substituted hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, hydrocarbylsulfido, silyl, germyl, hydride, phosphine, amine, sulfide, carbon monoxide, nitryl, or isonitryl ligand, and X is a halogen; (b) washing the poly(aryl)silane with a washing composition comprising water; and (c) contacting the poly(aryl)silane with an adsorbent sufficient to remove the metal from the poly(aryl)silane. Alternatively, the method may first form a polyarylsilane in catalytic dehydrocoupling step (a), then include the steps of (b′) reacting the polyarylsilane with (i) a halogen source and (optionally) a Lewis acid, or (ii) trifluoromethanesulfonic acid (HOTf), to form a halopolysilane; and (c′) reducing the halopolysilane with a metal hydride to form the polysilane of the formula H—[(AH₂)_(n)(c—A_(m)H_(pm−2))_(q)]—H. This latter embodiment may also produce a polysilane of the formula H—[(AH₂)_(n′−s)(AH[A_(a)H_(2a+1)])_(s)(c—A_(m)H_(pm−2))_(q′)]—H, where A, a, m, and p are as described above; n′ is independently an integer in the same range as n above; q′ is independently an integer in the same range as q above; and s is an integer less than n′ (generally from 1 to 3; e.g., 1).

The present invention is directed towards the synthesis of semiconductor inks via dehydrocoupling of (aryl)silanes and/or -germanes. Such synthesis allows for tuning of the ink properties (e.g., viscosity, boiling point, and surface tension) and for deposition of silicon films or islands by spincoating, inkjetting, dropcasting, etc., with or without the use of UV irradiation. Thus, the invention further relates to a method of making or forming a semiconductor film from the present ink composition, comprising the steps of: (A) spin-coating or printing the composition onto a substrate (optionally, with simultaneous or immediately subsequent UV irradiation); (B) heating the composition sufficiently to form an amorphous, hydrogenated semiconductor; and (C) annealing and/or irradiating the amorphous, hydrogenated semiconductor sufficiently to at least partially crystallize and/or reduce a hydrogen content of the amorphous, hydrogenated semiconductor and form the semiconductor film.

These and other advantages of the present invention will become readily apparent from the detailed description of preferred embodiments below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a first approach for the synthesis of polysilanes from arylsilane monomers by catalytic dehydrocoupling, halogenation, and reduction.

FIG. 2 is a diagram showing a second approach for the synthesis of polysilagermanes from arylsilane and arylgermane monomers by catalytic dehydrocoupling, halogenation, and reduction.

FIG. 3 is a diagram showing an approach for the synthesis of polycyclosilanes from cyclosilane monomers by catalytic dehydrocoupling alone.

FIG. 4 is a diagram showing an approach for the synthesis of poly(cyclo)silanes from arylsilane and cyclosilane monomers by catalytic dehydrocoupling, halogenation, and reduction.

FIG. 5 shows a GPC trace of a typical polyphenylsilane synthesized by an example of the present method.

FIGS. 6(A)-(C) show ¹H NMR spectra of an isolated polyphenylsilane (FIG. 6 a), polychlorosilane (FIG. 6 b), and polysilane (FIG. 6 c), synthesized by examples of the present method.

FIG. 7 is a graph showing the viscosity of exemplary polysilane inks as a function of the polysilane mass loading in the ink.

FIG. 8 is a typical SIMS profile of certain impurity atoms in an exemplary silicon film made by an example of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be readily apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, components, and circuits have not been described in detail so as not to unnecessarily obscure aspects of the present invention.

For the sake of convenience and simplicity, the terms “C_(a)—C_(b) alkyl,” “C_(a)—C_(b) alkoxy,” etc., shall refer to both branched and unbranched moieties, to the extent the range from a to b covers 3 or more carbon atoms. Unless otherwise indicated, the terms “arene,” “aryl,” and “ar-” refer to both mono- and polycyclic aromatic species that may be unsubstituted or substituted with one or more conventional substituents, to the extent possible and/or applicable. The prefixes “(per)alkyl” and “(per)hydro” refer to a group having from one to all of its bonding sites substituted with alkyl groups or hydrogen atoms, respectively (e.g., “(per)alkylsilyl” refers to a silyl group of n atoms having from 1 to 2n+1 alkyl groups bound thereto). The terms “silane,” “polysilane” and “(cyclo)silane” may be used interchangeably herein, and unless expressly indicated otherwise, these terms individually refer to a compound or mixture of compounds that consists essentially of (1) silicon and/or germanium and (2) hydrogen. The terms “arylsilane,” “polyarylsilane” and “aryl(cyclo)silane” may be used interchangeably herein, and unless expressly indicated otherwise, these terms refer to a compound or mixture of compounds that contains or consists essentially of units having a silicon and/or germanium atom, a hydrogen atom bound thereto, and an aryl group bound thereto, where the aryl group may be substituted by a conventional hydrocarbon, silane or germane substituent. The term “(aryl)silane” refers to a silane, polysilane or cyclosilane that may or may not contain an aryl or substituted aryl group bound thereto. The prefix “(cyclo)-” generally refers to a compound or mixture of compounds that may contain a cyclic ring, and the prefix “cyclo-” or “c-” generally refers to a compound or mixture of compounds that contain one or more cyclic rings. For the sake of briefness, the terms “halo-,” “halide” and grammatical derivations thereof may describe halogens as defined in the Periodic Table of Elements (F, Cl, Br, and I) and halogen-like species (e.g., that form stable monovalent anions) such as methanesulfonate (OMs), trifluoromethanesulfonate (OTf), toluenesulfonate (OTs), etc. Also, the terms “isolating” and “purifying” (and grammatical variations thereof) may be used interchangeably herein, but these terms are intended to have their art-recognized meanings, unless indicated otherwise.

The present invention concerns a polysilane compound, a “liquid silicon” ink composition containing the polysilane, methods for synthesizing the polysilane and for making the ink composition, and methods of using the polysilane and/or ink composition to make a semiconductor film. In general, the polysilane has the formula H—[(AHR)_(n)(c—A_(m)H_(pm−2)R′_(rm))_(q)]—H, where each instance of A is independently Si or Ge; each instance of R and R′ is independently H, —A_(a)H_(a+1)R² _(a) (where R² is H, aryl or substituted aryl), halogen, aryl or substituted aryl, but if q=0 and A is Si, R is not phenyl; (n+a)≧10 if q=0, q≧3 if n=0, and (n+q)≧6 if both n and q≠0; p is 1 or 2; (p+r)=2; and each instance of m is independently from 3 to 12. The composition generally comprises the polysilane compound (preferably where R, R′ and [to the extent present] R² are H) and a solvent in which the polysilane is soluble.

Even further aspects of the invention concern methods of making a polysilane generally comprising the steps of (a) combining a silane compound of the formula AH_(a)R¹ _(4−a), the formula A_(k)H_(g)R^(1′) _(h) and/or the formula c—A_(m)H_(pm)R^(1′) _(rm) with a catalyst of the formula R⁴ _(x)R⁵ _(y)MX_(z) (or an immobilized derivative thereof, or which may be synthesized in situ from the corresponding precursors) to form a poly(aryl)silane of the formula H—[(AHR¹)_(n)—(c—A_(m)H_((pm−2))R^(1′) _(rm))_(q)]—H, where A, R¹, k, g, h, p, q, R^(1′), M, R⁴, R⁵, x, y, z, and X are as described herein, and a=2 or 3; (b) washing the poly(aryl)silane with a washing composition comprising water; and (c) contacting the poly(aryl)silane with an adsorbent sufficient to remove the metal from the poly(aryl)silane. Alternatively, the method may first form a polyarylsilane in accordance with step (a), then include the steps of (b′) reacting the polyarylsilane with (i) a halogen source and (optionally) a Lewis acid, or (ii) trifluoromethanesulfonic acid (HOTf), to form a halopolysilane; and (c′) reducing the halopolysilane with a metal hydride to form the polysilane of the formula H—[(AH₂)_(n)—(c—A_(m)H_(pm−2))_(q)]—H.

The invention further relates to a method of making or forming a semiconductor film from the present ink composition, comprising the steps of: (A) spin-coating or printing the composition onto a substrate (optionally, with simultaneous or immediately subsequent UV irradiation); (B) heating the composition sufficiently to form an amorphous, hydrogenated semiconductor; and (C) annealing and/or irradiating the amorphous, hydrogenated semiconductor sufficiently to at least partially crystallize and/or reduce a hydrogen content of the amorphous, hydrogenated semiconductor and form the semiconductor film.

The invention, in its various aspects, will be explained in greater detail below with regard to exemplary embodiments.

An Exemplary Polysilane

In one aspect, the present invention relates to a polysilane having the formula H—[(AHR)_(n)(c—A_(m)H_(pm−2)R′_(rm))_(q)]—H, where each instance of A is independently Si or Ge; each instance of R and R′ is independently H, —A_(b)H_(b+1)R² _(b) (where R² is H, aryl or substituted aryl), halogen, aryl or substituted aryl, but if q=0 and A is Si, R is not phenyl; (n+b)≧10 if q=0, q≧3 if n=0, and (n+q)≧6 if both n and q≠0; p is 1 or 2; (p+r)=2; and each instance of m is independently from 3 to 12. In preferred embodiments, the polysilane has the formula H—(AHR)_(n)—H (i.e., where q=0) or H—(c—A_(m)H_(2m−2))_(q)—H (i.e., where n=0). However, as will be explained below (particularly with regard to FIG. 4), polysilanes having both cyclic blocks and linear/branched chains are contemplated. Thus, “n” and “q*m” may represent an average number of silicon and/or germanium atoms in the linear polysilane and in the polycyclosilane, respectively, according to or calculated from the number average molecular weight (Mn) of the polysilane. Furthermore, “n” may represent one or more blocks of substantially linear or branched chains of silicon atoms in the polysilane. Thus, in general, the polysilane may comprise a homopolymer of repeating —(—AHR—)—, —(—A_(k)H_(2k)—)— or —(c—A_(m)H_(2m−2))— units, or a block copolymer comprising one or more blocks of —(—AHR—)—, —(—A_(k)H_(2k)—)— and/or —(c—A_(m)H_(2m−2))— units, each of which may include one or more such units in a given block.

A first exemplary polysilane has the formula H—(AHR)_(n)—H, where each instance of A is independently Si or Ge; each instance of R is independently H, halogen, aryl, substituted aryl, or —A_(b)H_(b+1)R² _(b) (where R² is H, aryl or substituted aryl), but if A is Si, R is not phenyl; and (n+b)≧10. In general, the polysilane has a linear structure (i.e., where R is H, halogen, aryl when at least one A is Ge and aryl other than phenyl when A is Si only, or substituted aryl), but branched analogs (i.e., where R is —A_(b)H_(b+1)R² _(b)) are possible. Generally, such branched analogs will be present in a mixture with one or more linear polysilanes. In general, (n+b) and/or (n+qm) represent an average number of silicon and/or germanium atoms in the product mixture, and in most cases, that average number is less than or equal to about 50. For example, when the polysilane is linear, n≦50. However, under typical conditions and/or using certain known catalysts and/or monomers, (n+b) is more typically ≦25 or 30.

In certain embodiments of the polysilane of H—(AHR)_(n)—H, R is H, Cl, or tolyl (preferably H), and A is Si. However, in other embodiments, at least one A is Ge, and R may be phenyl. In such an embodiment, the polygermasilane is essentially a random and/or statistical mixture of polysilanes, polygermanes and polygermasilanes containing a proportion or ratio of germanium-to-silicon atoms that substantially corresponds to the proportion or ratio of the germanium monomer to silicon monomer in the mixture of starting materials, as may be more fully explained below.

In another aspect, the polysilane has the formula H—(c—A_(m)H_(2m−2))_(q)—H, where q≧3 (e.g., from 3 to 10); and each instance of m is independently from 3 to 12. In particular, m is generally from 5 to 8, and typically, most instances (e.g., more than 50%, 70% or 80%) of m will predominantly be 5.

The structure and nature of the present poly(aryl)silanes and poly(halo)silanes may be better understood with reference to some exemplary methods for their synthesis.

An Exemplary Method of Making Polyarylsilanes

In general, poly- and oligo-hydrosilane and -hydrogermane compounds for semiconductor inks can be synthesized by dehydrocoupling of arylhydrosilanes and/or arylhydrogermanes (R¹AH₃ or R¹ ₂AH₂, where R¹ is aryl and A=Si or Ge, to form linear, branched, cyclic, and/or caged arylhydrosilanes and/or arylhydrogermanes), followed by Lewis acid-catalyzed cleavage of the aryl groups and hydride reduction to yield linear, branched, cyclo-, and/or caged polysilanes, polygermanes or polysilagermanes. This aspect of the invention focuses on dehydrocoupling of arylhydrosilanes and/or arylhydrogermanes (R¹AH₃, where R¹ is aryl and A═Si or Ge).

Dehydrocoupling of arylhydrosilanes using titanium (Ti), zirconium (Zr), hafnium (Hf), neodymium (Nd) and uranium (U) catalysts is known (see, e.g., T. D. Tilley, Acc. Chem. Res. 1993, vol. 26, pp. 22-29; V. K. Dioumaev and J. F. Harrod, J. Organomet. Chem. vol. 521 [1996], pp. 133-143; and Q. Wang and J. Y. Carey, Can. J. Chem. vol. 78 [2000], pp. 1434-1440). In part, the present invention relates to use of this approach to synthesize novel polyarylhydrosilanes, -germanes and/or -silagermanes, and to an improved method for synthesizing polyarylhydrosilanes, -germanes and/or -silagermanes that eliminates the metal catalyst to a significantly greater degree than alternative approaches, thereby significantly improving the stability of subsequently-produced polyhydrosilanes, -germanes and/or -silagermanes.

Thus, in one aspect, the present invention relates to a method of making a polysilane, comprising (a) combining a silane compound of the formula AH_(a)R¹ _(4−a), the formula A_(k)H_(g)R^(1′) _(h) and/or the formula c—A_(m)H_(pm)R^(1′) _(rm) with a catalyst of the formula R⁴ _(x)R⁵ _(y)MX_(z) (or an immobilized derivative thereof, or which can be synthesized in situ from corresponding precursors) to form a poly(aryl)silane of the formula H—[(AHR¹)_(n)—(c—A_(m)H_((pm−2))R^(1′) _(rm))_(q)]—H, where each instance of A is independently Si or Ge, a=2 or 3, and each instance of R¹ and R^(1′) is independently aryl, substituted aryl, or —A_(b)H_(b+1)R² _(b) (where R² is aryl or substituted aryl); (n+b)≧10 if q=0, q≧3 if n=0, and (n+q)≧6 if both n and q≠0; k is an integer of from 2 to 12, g≧2 and (g+h)=2k+2; p is 1 or 2, m is an integer of from 3 to 12, p is 1 or 2, and r is 0 or 1; R^(1′) is the same as R¹, except that when R¹ is —A_(b)H_(b+1)R² _(b), R¹ may be H; M is a metal selected from the group consisting of Ti, Zr and Hf, x=1 or 2, y=1, 2 or 3, z=0, 1 or 2, 3≦(x+y+z)≦8, each of the x instances of R⁴ is independently a substituted or non-substituted cyclopentadienyl, indenyl, fluorenyl, siloxyl, germoxyl, hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, or hydrocarbylsulfido ligand; each of the y instances of R⁵ is independently a substituted or non-substituted hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, hydrocarbylsulfido, silyl, (per)alkylsilyl, germyl, (per)alkylgermyl, hydride, phosphine, amine, sulfide, carbon monoxide, nitryl, or isonitryl ligand, and X is a halogen; (b) washing the poly(aryl)silane with a washing composition comprising water; and (c) contacting the poly(aryl)silane with an adsorbent sufficient to remove the metal (i.e., from the catalyst) from the poly(aryl)silane.

In the first exemplary embodiment of the present method, the silane compound has the formula AH_(a)R¹ _(4−a). In preferred implementations of this embodiment, A is Si, R¹ is phenyl or tolyl, and/or a is 3. However, compounds of the formula A_(k)H_(g)R^(1′) _(h) (particularly where k is an integer of at least 2, g=k, [k+2], 2k or [2k+2], and h=0, 2, or k) are likely to be present in the dehydrocoupling reaction mixture. As a result, the present method contemplates use of compounds of the formula A_(k)H_(g)R^(1′) _(h) for making poly(aryl)silanes.

Preferably, the metal M in the dehydrocoupling catalyst is Zr or Hf. These metals tend to provide a sufficient balance between dehydrocoupling rate or activity, poly(aryl)silane molecular weight and content of cyclosilane by-products (e.g., Hf generally produces a higher proportion of linear polysilane products than Zr). In various embodiments, x is 2 and R⁴ is cyclopentadienyl (Cp), permethyl-cyclopentadienyl (Cp*), indenyl or fluorenyl (Fl). Having at least one bulky or substituted cyclopentadienyl ligand (e.g., Cp*, indenyl or fluorenyl) tends to promote dehydrocoupling by reducing a tendency of the catalyst to dimerize, but the catalyst is not at all required to have such a ligand. Also, in various embodiments, y is 2 and R⁵ in the dehydrocoupling catalyst is H, C₁-C₆ alkyl, C₆-C₁₂ aryl, SiR² ₃, or Si(SiR² ₃)₃, where R² is H or C₁-C₄ alkyl. Such ligands are believed to promote metathesis of Si—H or Ge—H bonds in the starting silane compound.

Generally, the washing composition in this embodiment of the present method comprises deionized water or dilute aqueous acid. For example, the aqueous acids suitable for use in the present method generally include the mineral acids and their equivalents, such as hydrochloric acid, hydrobromic acid, trifluoroacetic acid, and trifluoromethanesulfonic acid. Preferably, the aqueous acid comprises hydrochloric acid. The dilution factor for the washing composition may be from 1:1 to 1:1000 (concentrated mineral acid to water), generally by volume. For example, the dilute aqueous acid may comprise from 0.1 to 10 vol. % (e.g., from 1 to 5 vol. %) of conc. HCl in deionized water. In a preferred implementation, the present washing step comprises washing the poly(aryl)silane one or more times with dilute aqueous acid, followed by washing the acid-washed poly(aryl)silane one or more times with water.

In general, to further remove the metal from the poly(aryl)silane, a solution of the poly(aryl)silane in a suitable organic solvent (typically the washed poly[aryl]silane) is contacted with the adsorbent for a length of time sufficient for the adsorbent to adsorb the metal from the catalyst. The adsorbent generally comprises a chromatography gel or finely divided silicon and/or aluminum oxide that is substantially unreactive with the polyarylsilane. Examples of suitable adsorbents include silica gel, alumina, FLUORISIL, and CELITE. In one embodiment, such contacting comprises passing the poly(aryl)silane through a column packed with the adsorbent. Alternatively, a solution of the poly(aryl)silane may be mixed with the adsorbent for a length of time sufficient for the adsorbent to adsorb the metal/catalyst from the solution. The adsorbent is generally removed from the adsorption mixture by conventional filtration.

FIG. 1 shows a first exemplary scheme illustrating dehydrocoupling of PhSiH₃, followed by Lewis acid-catalyzed chlorination and reduction. Dehydrocoupling of PhSiH₃ generally forms polyphenylsilane 20 and a relatively small proportion of cyclic silane compounds such as cyclopentaphenylsilane (c—(SiHPh)₅ 25). Although the polyphenylsilane 20 may be separated and/or isolated from the cyclopentaphenylsilane and/or other cyclic silane compounds, the cyclic silane compounds such as c—(SiHPh)₅ 25 generally do not affect subsequent steps in the synthesis of polysilanes (see, e.g., the formation of semiconducting films discussed below). The dehydrocoupling reaction evolves hydrogen gas, and thus, tends to be irreversible if the hydrogen gas is removed from the dehydrocoupling reaction vessel. Generally, the polymerization/dehydrocoupling reaction time is from a few hours (e.g., 3, 4, 6 or more hours) to a few days (e.g., 3, 4 or 5 days). The reaction mixture may be formed by dropwise addition of the monomer to a solution of the catalyst, or by mixing the catalyst directly with the monomer. In fact, neat solutions of silane/germane monomer and catalyst tend to provide higher molecular weights (e.g., number average molecular weights, or Mn) of polyarylsilane 20. The reaction temperature is also kept relatively low (e.g., from about 0 to about 30° C.), generally to promote higher polyarylsilane 20 molecular weights and/or to reduce the amount of cyclic silane compound. However, in some cases (e.g., when a sterically crowded catalyst and/or monomer is/are used), a higher temperature may be advantageous for increasing the reaction rate.

As shown in FIG. 1, the dehydrocoupling catalyst Cp₂ZrPh₂ may be generated in situ from a zirconocene halide (e.g., Cp₂ZrCl₂) and an alkyl, aryl or peralkylsilyl metal reagent (e.g., PhMgBr, which can also be generated in situ in accordance with known techniques). Dehydrocoupling catalysts include complexes of Ti, Zr, and/or Hf, in an oxidation state of +4, +3, and/or +2, and having a general formula R⁴ _(x)R⁵ _(y)MX_(z), where M═Ti, Zr, or Hf; x=1 or 2, y=2 or 3, z=0, 1 or 2, 3≦(x+y+z)≦8 (which may depend on the coordination sites available on M, as is known in the art), each of the x instances of R⁴ is independently a substituted or non-substituted cyclopentadienyl, indenyl, fluorenyl, siloxyl, germoxyl, hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, or hydrocarbylsulfido ligand; each of the y instances of R⁵ is independently a substituted or non-substituted hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, hydrocarbylsulfido, silyl, germyl, hydride, phosphine, amine, sulfide, carbon monoxide, nitryl, or isonitryl ligand; and X is a halogen (e.g., Cl, Br, OTf, ClO₄, etc.).

Further, the metal M, or one or more of the x instances of R⁴, y instances of R⁵ or z instances of X, can be independently bound to a silica, alumina, or polymer surface rendering the catalyst heterogeneous. The polymer is typically a hydrocarbon polymer, such as polyethylene, polypropylene, polystyrene, a polyethylene-polypropylene or polyethylene-polystyrene copolymer, etc.

Alternative catalysts can include any conventional dehydrocoupling catalyst, especially those containing a Group 4 element. For example, an Hf analog of the Zr catalyst in FIG. 1 will generally reduce the amount of cyclic silane compounds produced. Also, as mentioned above, metallocene catalysts containing a relatively bulky ligand, such as CpCp*Zr(SiMe₃)Ph, may provide higher molecular weight polyphenylsilanes (e.g., having a Mn as high as 5000 Daltons [i.e., n≈25-45], whereas the Mn of the polyphenylsilane 20 produced using Cp₂ZrPh₂ is generally around 1200 Daltons [i.e., n≈10-12]). Use of a sterically crowded catalyst like CpCp*Zr(SiMe₃)Ph is expected to produce a higher viscosity polysilane ink composition.

The starting material(s) and/or substrates generally include silicon and germanium compounds of the general formula R¹AH₃ or R¹ ₂AH₂, where A is Si or Ge, and R′ is aryl or substituted aryl. Use of tolylsilane (CH₃C₆H₄SiH₃) as a monomer instead of phenylsilane (PhSiH₃) may be advantageous for subsequent steps in the polysilane synthesis. Tolylsilane (and oligomers thereof) are generally easier to chlorinate (e.g., cleave the C—Si bond with HCl and a Lewis acid such as AlCl₃), thereby presumably reducing aromatic impurities in any subsequently synthesized polysilane.

Typical conditions for dehydrocoupling reaction include a temperature of about ambient or room temperature, a pressure of about atmospheric pressure (or about 1 atm) of inert gas under dynamic conditions (e.g., in a reaction vessel having somewhat free gas out-flow, such as a gas bubbler, generally to allow escape of evolved hydrogen gas). The typical catalyst loading may be >1 mol % (e.g., from 1 to 10 mol %, 2 to 5 mol %, or any range of values therein, relative to the molar quantity of monomer) for dehydrocoupling of arylsilanes and arylgermanes.

The adsorbing step in the present method is generally used to remove the metal of the catalyst (e.g., Zr in FIG. 1) from the polyphenylsilane 20. Conventional chromatography methods using gels, such as FLORISIL, and other gels like silica, alumina, and CELITE are generally suitable. Alternatively, the gel is added to a polyphenylsilane 20 solution and stirred (generally for a length of time sufficient to remove some or substantially all of the metal from the solution), then the gel is generally removed by filtration. Contacting a chromatography gel with a solution of the polyphenylsilane 20 can be substituted by simply passing the solution of polyphenylsilane 20 through a thick pad of the gel.

The solvents used in the procedure are not limited. Cyclohexane, toluene, and diethyl ether are generally preferred, although any solvent or mixture of solvents with relatively low boiling points (e.g., ≦100° C., ≦80° C., or ≦60 ° C.), compatible with polysilanes, are suitable.

FIG. 2 shows a second exemplary scheme illustrating dehydrocoupling of PhSiH₃ and PhGeH₃, followed by chlorination and reduction. Generally, a mixture of arylsilane (e.g., PhSiH₃) and arylgermane (PhGeH₃) are dehydrocoupled using a diaryl-, bis(peralkylsilyl)-, aryl(peralkylsilyi)-, dialkyl- or alkyl(peralkylsilyl) metallocene catalyst such as Cp₂ZrPh₂ to provide a polyphenylsilagermane 110 of the formula H—(SiHPh)_(n)(GeHPh)_(m)—H, where (n+m)≧10. In the polyphenylsilagermane 110 product, n and m generally represent a random and/or statistical mixture corresponding to the molar ratio of PhSiH₃ to PhGeH₃ in the dehydrocoupling reaction mixture. Thus, m may be anywhere from 1 to (n−1), but more typically, the molar ratio of PhSiH₃ to PhGeH₃ is anywhere from 1:1 to 20:1, and thus, m will typically be an integer of from 1 to n. The product mixture containing polyphenylsilagermane 110 may also include cyclic and linear/branched polyphenylsilanes and -germanes. No significant and/or detectable heterocoupling may occur in such cyclic byproducts in the synthetic approach of FIG. 2.

An Exemplary Method of Making Polysilanes

Cleavage of aryl groups bound to Si or Ge, and reduction of silicon and/or germanium halides and pseudo-halides are generally disclosed in, e.g., U.S. Pat. Nos. 7,498,051, 7,314,513, and 7,674,926; and U.S. patent application Ser. No. 10/950,373 , filed Sep. 24, 2004, the relevant portions of which are incorporated herein by reference. Typically, and as shown in FIGS. 1 and 2, this cleavage reaction is conducted with HCl and AlCl₃. However, as is also known, a conventional chlorination-based cleavage reaction can be substituted with HBr to obtain a polybromosilane, or with TfOH to obtain a poly(trifluoromethanesulfonyl)silane. Thus, the present invention also relates to the combination of (1) catalytic dehydrocoupling as described above and (2) the cleavage and reduction processes described herein, to synthesize polyhydrosilanes, -germanes and/or -silagermanes.

Thus, in another aspect, the present invention concerns a method of making a polysilane, comprising the steps of (a) combining a silane compound of the formula AH_(a)R¹ _(4−a), the formula A_(k)H_(g)R¹ _(h) and/or the formula c—A_(m)H_(pm)R^(1′) _(rm) with a catalyst of the formula R⁴ _(x)R⁵ _(y)MX_(z) (or an immobilized derivative thereof) to form a polyarylsilane of the formula H—[(AHR¹)_(n)(c—A_(m)H_((pm−2))R^(1′) _(rm))_(q)]—H as described above, where each instance of A is independently Si or Ge, a=2 or 3, each instance of R¹ and R^(1′) is independently aryl, substituted aryl, or —A_(b)H_(b+1)R_(b) (where R is aryl or substituted aryl); (n+b)≧10 if q=0, q≧3 if n=0, and (n+q)≧6 if both n and q≠0; p is 1 or 2; k is an integer of from 2 to 12, g≧2 and (g+h)=2k+2; each instance of m is independently from 3 to 12; M is a metal selected from the group consisting of Ti, Zr and Hf; x=1 or 2; y=1, 2 or 3; z=0, 1 or 2; 3≦(x+y+z)≦8; each of the x instances of R⁴ is independently a substituted or non-substituted cyclopentadienyl, indenyl, fluorenyl, siloxyl, germoxyl, hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, or hydrocarbylsulfido ligand; each of the y instances of R⁵ is independently a substituted or non-substituted hydrocarbyl, hydrocarbyloxy, hydrocarbylamino, hydrocarbylsulfido, silyl, germyl, hydride, phosphine, amine, sulfide, carbon monoxide, nitryl, or isonitryl ligand; and X is a halogen; (b) reacting the polyarylsilane with (i) a halogen source and (optionally) a Lewis acid or (ii) trifluoromethanesulfonic acid (HOTf), to form a halopolysilane; and (c) reducing the halopolysilane with a metal hydride to form a polysilane of the formula H—[(AH₂)_(n)(c—A_(m)H_(pm−2))_(q)]—H.

Generally, the method comprises combining a silane compound of the formula AH_(a)R¹ _(4−a) with a catalyst of the formula R⁴ _(x)R⁵ _(y)MX_(z) to form a polyarylsilane of the formula H—(AHR¹)_(n)—H. However, as described above, compounds of the formula A_(k)H_(g)R^(1′) _(h) (particularly where k is an integer of at least 2, g=2, [k+2], 2k or [2k+2], and h=0, 2 or k, depending on the structure of the silane starting compound) are likely to be present in the dehydrocoupling reaction mixture. As a result, the present method contemplates use of compounds of the formula A_(k)H_(g)R^(1′) _(h) for making polyarylsilanes. Also, in certain embodiments, the method comprises reacting the polyarylsilane with the halogen source and the Lewis acid, wherein the Lewis acid comprises a compound of the formula M³ _(v)X² _(w), where M³ comprises a member selected from the group consisting of transition metals and Group IIIA elements; v is 1 or 2; X² comprises a halogen; and w is any integer up to the number of ligand binding sites available on the v instances of M³. In a preferred embodiment, M³ comprises Al, and X² is Cl or Br (e.g., Cl, as shown in FIGS. 1-2).

In further embodiments of the present method, the metal hydride comprises a compound of the formula M¹ _(a)M² _(b)H_(c)R⁶ _(d), where M¹ and M² are independently first and second metals, each R⁶ in the metal hydride compound is independently a ligand bound to at least one of M¹ and M² m by a covalent, ionic or coordination bond, at least one of a and b is at least 1, c is at least 1, and d is 0 or any integer up to one less than the number of ligand binding sites available on the (a+b) instances of M¹ and M². In certain implementations, the metal hydride comprises a member of the group consisting of lithium aluminum hydride (LAH, as shown in FIGS. 1-2), calcium aluminum hydride, sodium borohydride, aluminum hydride, gallium hydride, and aluminum borohydride.

Referring to FIGS. 1-2, the procedure for Lewis acid-catalyzed halogenation (e.g., treatment or reaction of polyarylsilane 20 or polyarylsilagermane 110 with HCl and AlCl₃ in an inert organic solvent such as cyclohexane) is largely as described in U.S. Pat. No. 7,498,015. However, exemplary variations of the procedure include a halogenation (e.g., chlorination) by bubbling HX gas (e.g., dry HCl) through a solution of polyarylsilane 20 or polyarylsilagermane 110 and Lewis acid for a length of time of from 30 min. to about 6 hours to form polychlorosilane 30 or polychlorosilagermane 120, respectively, and reduction using a metal hydride reducing reagent (not limited to lithium aluminum hydride [LAH], although LAH as shown in FIGS. 1 and 2 is a preferred metal hydride reducing reagent) for a length of time of from about 1 hour, 2 hours or 4 hours to about 8, 12, or 16 hours (e.g., overnight). Other exemplary metal hydride reducing agents are disclosed in U.S. Pat. Nos. 7,498,015, 7,314,513, and 7,674,926, and U.S. patent application Ser. No. 10/950,373 , the relevant portions of which are incorporated herein by reference. Also, the reagent addition sequence preferably comprises adding a solution of metal hydride (e.g., LAH) in an inert organic solvent (e.g., dry diethyl ether) to a stirred solution of polychlorosilane 20 or polychlorosilagermane 120. Workup is generally as described in U.S. Pat. Nos. 7,498,015, 7,314,513, and 7,674,926, and U.S. patent application Ser. No. 10/950,373, the relevant portions of which are incorporated herein by reference.

A Second Exemplary Method for Making Oligo- and/or Polysilanes

In another aspect, the present invention concerns a method of making oligo- and/or polysilanes that includes simply a dehydrocoupling step (e.g., dehydrocoupling of perhydrosilanes and/or perhydrogermanes; e.g., linear, branched, cyclo-, or caged hydrosilanes and/or hydrogermanes), such as the exemplary reaction scheme of FIG. 3. FIG. 3 shows an exemplary scheme illustrating dehydrocoupling of cyclo-Si₅H₁₀ 15 to form poly(cyclopentasilane) 200. Generally, the same dehydrocoupling catalyst (e.g., α-fluorenyl-α,α-dimethylsilylfluorenyl dibutylzirconium, or [Fl₂SiMe₂]ZrBu₂, generated in situ as shown in FIG. 3) as described above may be used for dehydrocoupling cyclosilanes. For dehydrocoupling of c—Si₅H₁₀, typical catalyst loading may be <0.1 mol % (e.g., from 0.0001 to 0.1 mol %, 0.001 to 0.05 mol %, or any range of values therein), relative to the amount of monomer (e.g., c—Si₅H₁₀).

Thus, the present invention further concerns a method of making an oligo- and/or polysilane, comprising (1) combining a silane compound of the formula c—A_(m)H_(pm) and/or the formula A_(k)H_(2k+2) with a catalyst of the formula R⁴ _(x)R⁵ _(y)MX_(z) (or an immobilized derivative thereof, or which may be synthesized in situ from corresponding precursors) to form a polysilane of the formula H—(A_(k)H_(2k))_(q′)—(c—A_(m)H_(pm−2))_(q)—H, where each instance of A is independently Si or Ge, q′+q ≧3, p is 1 or 2, k is an integer of from 2 to 12, m is an integer of from 3 to 12, and M, x, y, z, R⁴, R⁵, and X are as described above; (2) washing the polysilane with a washing composition comprising water; and/or (3) contacting the polysilane with an adsorbent sufficient to remove the metal from the polysilane.

In further embodiments of the approach exemplified in FIG. 3, A is independently Si or Ge, q≧3, p is 1 or 2, and/or m is from 3 to 12 (preferably from 5 to 8). In addition, linear and/or branched silanes of the general formula A_(k)H_(2k+2) (where k is from 1 to 12, preferably from 5 to 10 [e.g., for homogeneous synthesis] or from 1 to 4 [e.g., for heterogeneous synthesis]) may be added to the dehydrocoupling reaction mixture to form polysilanes of the formula H—[(AHR*)_(n)]_(t)—(c—A_(m)H_(pm−2))_(q)]—H, where R* is H or —A_(b)H_(2b+1)R_(b) (preferably H), each of the t instances of n are independently from 1 to 12 (preferably from 3 to 12, more preferably from 5 to 10), each of the t*n instances of b are independently from 1 to 6 (preferably from 1 to 4), t*(n+b)≧4 (preferably ≧6 and more preferably ≧10), and m, p and q are as described above.

A Third Exemplary Method for Making Oligo- and/or Polysilanes

In another aspect, the present invention concerns oligo- and/or polysilanes containing both linear and cyclic portions and a method of making the same, based on catalytic dehydrocoupling (e.g., dehydrocoupling of [aryl]silanes and/or [aryl]germanes with cyclosilanes and/or cyclogermanes), such as the exemplary reaction scheme of FIG. 4. FIG. 4 shows an exemplary scheme illustrating dehydrocoupling of phenylsilane (PhSiH₃) with cyclo-Si₅H₁₀ 15 to form block copolymer or linear/branched poly(phenylsila)(cyclopentasilylene) 320. Generally, the same dehydrocoupling catalyst (e.g., bis[cyclopentadienyl] diphenylzirconium or [Fl₂SiMe₂]ZrBu₂, as shown in FIGS. 1-3) as described above may be used for dehydrocoupling arylsilanes with cyclosilanes. Linear or branched perhydrosilanes can be substituted for or added to the cyclosilanes, to provide a greater degree of branching or to possibly increase the average number of silicon atoms in the polymer/oligomer. Also, cyclosilanes with an exocyclic silyl group (e.g., cyclo-[(SiPhH)₄SiH]—[SiH₃]) are also contemplated for use in the invention, and this are encompassed by the formula “c—A_(m)H_(pm).” The subscript “n” generally represents an average of the number of silicon atoms in the polysilane, and in this aspect of the invention, further represents two or more blocks of substantially linear or branched silicon chains in the polysilane.

Thus, the present invention further concerns a method of making an oligo- and/or polysilane, comprising (I) combining a silane compound of the formula c—A_(m)H_(pm) and/or the formula A_(k)H_(2k+2) with a silane monomer of the formula AH₃R¹ and a catalyst of the formula R⁴ _(x)R⁵ _(y)MX_(z) (or an immobilized derivative thereof, or which may be synthesized in situ from corresponding precursors) to form a block or branched polyarylsilane of the formula H—[(AHR¹)_(n)]_(u)—(A_(k)H_(2k))_(q′)—(c—A_(m)H_(pm−2))_(q)—H, where each instance of A, R¹ and n are as described herein, u=(q′+q) or (q′+q)±1, q′+q≧3, p is 1 or 2, k is an integer of from 2 to 12, m is an integer of from 3 to 12, and M, x, y, z, R⁴, R⁵, and X are as described above; (II) reacting the block or branched poly(aryl)silane with (i) a halogen source and (optionally) a Lewis acid or (ii) trifluoromethanesulfonic acid (HOTf), to form a block or branched halopolysilane; and (c) reducing the block or branched halopolysilane with a metal hydride to form a polysilane of the formula H—[(AH₂)_(n)]_(u)—(A_(k)H_(2k))_(q′)—(c—A_(m)H_(pm−2))_(q)—H. In further embodiments of the approach exemplified in FIG. 4, A is Si, q′ is 0, p is 2, and/or m is from 5 to 8 (preferably 5 or 6).

An Exemplary Polysilane Composition and/or Semiconductor Ink

A further aspect of the present invention relates to a composition, comprising the present polysilane and a solvent in which the polysilane is soluble. Preferably, the solvent is one that is easily removed (and/or substantially completely removable) from the composition, and may be selected from the group consisting of linear alkanes, cycloalkanes, polycycloalkanes, (cyclic) siloxanes and fluoroalkanes. The (cyclic) siloxane solvents are generally those that are liquid at ambient temperatures (e.g., 15-30° C.), and may be selected from siloxanes of the formula (R₃Si)(OSiR₂)_(p)(OSiR₃) and cyclosiloxanes of the formula (SiR′₂O)_(q), where p is from 0 to 4, q is from 2 to 6 (preferably from 3 to 5), each R and R′ is independently H, C₁-C₆ alkyl, benzyl or phenyl substituted with from 0 to 3 C₁-C₄ alkyl groups (preferably R and R′ are methyl). The fluoroalkane may be selected from C₃-C₈ fluoroalkanes substituted with from 1 to (2m+2) fluorine atoms and that are liquid at ambient temperatures, where m is the number of carbon atoms in the fluoroalkane. More preferably, the solvent may be selected from the group consisting of C₆-C₁₂ monocycloalkanes and C₁₀-C₁₄ di- or tricycloalkanes (e.g., decalin). Preferably, the solvent is a C₆-C₁₀ cycloalkane (e.g., cyclohexane, cycloheptane, cyclooctane, etc.).

In the present ink composition, the polysilane is present in an amount of from about 0.5 to about 50%, preferably 5 to about 30% (more preferably from about 10 to about 20%) by weight or by volume. Of course, when the polysilane is in a liquid phase at room temperature, it may be used neat if its viscosity (and/or other physical and/or chemical properties) are suitable for printing and/or coating processes. Suitable ink formulations are disclosed in U.S. Pat. Nos. 7,503,236, 7,498,051, 7,314,513, and 7,674,926; and U.S. patent application Ser. No. 10/950,373, filed Sep. 24, 2004, the relevant portions of which are incorporated herein by reference. In the present case, the present polysilane may be substituted in part or entirely for the (cyclo)silane and/or hetero(cyclo)silane described in U.S. Pat. Nos. 7,503,236, 7,498,051, 7,314,513, and 7,674,926; and U.S. patent application Ser. No. 10/950,373.

An Exemplary Method for Making a Semiconductor Film

A further aspect of the invention relates to a method of forming a semiconductor film from the present composition, comprising the steps of (A) spin-coating or printing the composition onto a substrate (optionally, with simultaneous or immediately subsequent UV irradiation); (B) heating the composition sufficiently to form an amorphous, hydrogenated semiconductor; and (C) annealing and/or irradiating the amorphous, hydrogenated semiconductor sufficiently to at least partially crystallize and/or reduce a hydrogen content of the amorphous, hydrogenated semiconductor and form the semiconductor film. Preferably, the method of forming a semiconductor film comprises printing (e.g., inkjetting) the composition onto a substrate (e.g., a conventional silicon wafer, glass plate, ceramic plate or disc, plastic sheet or disc, metal foil, metal sheet or disc, or laminated or layered combination thereof, any of which may have an insulator layer such as an oxide layer thereon), and/or irradiating the amorphous, hydrogenated semiconductor with a sufficient dose of laser radiation to crystallize and/or electrically activate the amorphous, hydrogenated semiconductor and form the semiconductor film.

In the present method, it may be advantageous to irradiate the composition during deposition onto the substrate. Generally, as long as the ink composition is irradiated reasonably shortly after deposition (e.g., spincoating), it has a viscosity sufficient to form a film or layer on the substrate that does not bead up, disproportionate or otherwise substantially adversely affect the uniformity of a subsequently formed semiconductor film. Such irradiation of a coated and/or printed film prior to curing may provide further control of the film drying process, e.g., by increasing the viscosity of the ink composition after deposition. For example, the present composition (e.g., prior to deposition) may have a viscosity of from 2.5 to 20 cP, 3 to 12 cP, or any range of values therein.

Suitable methods for forming a semiconductor film are disclosed in U.S. Pat. Nos. 7,503,236, 7,314,513, and 7,619,248; and U.S. patent application Ser. No. 11/203,563, filed Aug. 11, 2005, the relevant portions of which are incorporated herein by reference. In the present case, the present polysilane ink composition may be substituted in part or entirely for the (cyclo)silane and/or hetero(cyclo)silane ink composition described in U.S. Pat. Nos. 7,503,236, 7,314,513, and 7,619,248; and U.S. patent application Ser. No. 11/203,563. The first heating and/or annealing step may comprise (i) “soft” curing the printed or coated ink composition, generally at a temperature of ≦200° C., ≦150° C., ≦120° C. or any maximum temperature in that range, sufficiently to remove volatile components (e.g., solvent, volatile silane compounds, etc.) and/or to further polymerize the silane film, and (ii) “hard” curing the film, generally at a temperature of ≦600° C., ≦500° C., ≦450° C. or any maximum temperature in that range, sufficiently to form a hydrogenated, amorphous silicon film. Generally, to obtain the most commercially valuable electrical activity and/or characteristics, the film is crystallized by heating in a furnace or irradiating with a dose of laser radiation sufficient to partly or substantially completely crystallize the hydrogenated, amorphous silicon film (e.g., form a polycrystalline silicon film). The use of laser radiation for crystallization advantageously includes a further annealing step to reduce the hydrogen content of the hydrogenated, amorphous silicon film prior to laser irradiation.

The described polysilanes and polysilane inks may also be used for the formation of doped silicon films. For example, an ink composition comprising the present polysilane may be printed or coated (optionally, with simultaneous or immediately subsequent UV irradiation) onto a substrate, converted to an amorphous or (partially) polycrystalline silicon film and subsequently doped, e.g., by conventional ion implantation or other doping technique such as ion showering or use of conventional spin-on-dopants (and optionally, subsequent annealing). Alternatively, the present ink composition may be further mixed with one or more dopants of the formula D_(a)H_(b) and/or D_(a)R⁶ _(b′) (where D is Sb, As, P or B; a is from 1 to 20; b is from 0 to 26; each of the b′ instances of R⁶ is independently H, alkyl, aryl, aralkyl or AR^(2′) ₃, where R^(2′) is hydrogen, alkyl, aryl, aralkyl or A_(y)H_(2y+1) [e.g., where 1≦y≦4, such as SiH₃ and Si(SiH₃)₃]; and b′ is an integer corresponding to the number of binding sites available on the a instances of D) and/or one or more doped silane and/or germane compounds of the formula (R^(2′) ₃A)_(r)A_(c)(DR⁶ ₂)_(s) (where D, a, R^(2′) and R⁶ are as described for the dopant; c is 1 to 4, r+s==2c+2, and s≧1 [preferably s≧3]) in an amount sufficient to provide a predetermined doping level or concentration and/or electrical characteristics in the electrically active film within a predetermined range of values. Such dopants, doped silanes and germanes, and others are disclosed in U.S. Pat. No. 7,314,513, the relevant portions of which are incorporated herein by reference.

Coating may comprise spin coating, inkjetting, dip-coating, spray-coating, slit coating, extrusion coating, or meniscus coating the ink composition onto a substrate. Preferably, coating comprises spin coating. Printing may comprise inkjetting or gravure, flexographic, screen or offset printing the ink in locations on the substrate corresponding to active transistor regions. After drying and/or heating the printed/coated film to remove any solvents and/or cure the film, and optionally irradiating the film (e.g., to fix the silanes to the substrate and/or to each other), the resulting semiconductor film/layer generally has an amorphous morphology, and before further processing, it is generally annealed (e.g., to reduce the hydrogen content of the polysilane) and crystallized (e.g., by heating or by laser irradiation; see, e.g., U.S. Pat. No. 7,314,513, and U.S. patent application Ser. No. 10/950,373, filed Sep. 24, 2004, the relevant portions of which are incorporated herein by reference). In many cases, such crystallization will also activate at least some of the added dopant.

One may also induce crystallization (in addition to activating some or all of the dopant) using conventional metal-promoted (re)crystallization. Suitable metal-based crystallization promoters and processes for their use in crystallizing an amorphous semiconductor film (e.g., as formed from semiconductor nanoparticles containing Si and/or Ge) may be disclosed in application Ser. No. 10/339,741, filed Jan. 8, 2003, now U.S. Pat. No. 7,078,276, and entitled “Nanoparticles and Method for Making the Same”,the relevant portions of which are incorporated herein by reference.

EXPERIMENTAL EXAMPLES

General Procedures

Standard Schlenk techniques were used for all synthesis and sample manipulations. A grease-free reaction setup utilizing threaded Teflon stopcocks was generally used to reduce contamination. Glassware was dried overnight at 120° C. in an oven before use. ¹H NMR and ²⁹Si NMR were measured by Acorn INC using d₆-benzene or d₁₂-cyclohexane as solvent. The molecular weight of polyphenylsilane was analyzed by Scientific Polymer Products, Inc., using Phenomenex phenogel columns. Elemental analyses were carried out by Desert Analytics.

Solvents and reagent purification. Toluene was purified by shaking twice with cold conc. H₂SO₄ (100 ml acid per L solvent), once or twice with water, once with aqueous 5% NaHCO₃, and again with water. Carbonyl-containing impurities were then removed by percolation through a Celite column impregnated with 2,4-dinitrophenylhydrazine, phosphoric acid and H₂O. The washed toluene was then dried over 4 Å molecular sieves overnight, and was distilled fresh to remove high boiling point residue.

Cyclohexane was first washed with conc. H₂SO₄ until the washings were colorless, followed by washing with alkaline potassium permanganate until the purple color of potassium permanganate did not change. Carbonyl-containing impurities were then removed by percolation through a Celite column impregnated with 2,4-dinitrophenylhydrazine, phosphoric acid and H₂O. The washed cyclohexane was then dried with activated 4 Å molecular sieves overnight and distilled over sodium (under argon).

Inhibitor-free diethyl ether was passed through a column of activated alumina (100 g Al₂O₃/1 L of ether), dried over lithium aluminum hydride (LAH) overnight, and freshly distilled under argon. DME (1,2-dimethoxyethane) was purified using the same method as for purifying ether.

PhSiH₃ (Gelest) was dried over 4 Å molecular sieves overnight, and then distilled under argon. AlCl₃ was purified by sublimation at 160° C. under vacuum.

LAH used for the chlorosilane reductions was purified from 1M LAH/ether solution (Aldrich). The purification procedure for obtaining 40 ml of purified 1M LAH ether solution is as follows: 40 ml of purified cyclohexane was added to 40 ml commercial 1 M LAH/ether solution. The mixture was concentrated by removing the ether under vacuum, and at the same time, white LAH precipitated out. The LAH was isolated by centrifugation, decanting the cyclohexane, and washing with 40 ml purified cyclohexane. The obtained white LAH was re-dissolved in 40 ml freshly purified ether, and 40 ml purified cyclohexane was added to the solution. The precipitation, centrifugation, and purified cyclohexane washing steps were repeated again to get purified LAH powder. 36 ml purified ether was added to the purified LAH to make 1M LAH/ether solution.

To obtain high purity polysilane, the purity of the solvents and the commercial LAH/ether solution or LAH powder is important. After employing the solvent and reagent purification procedures described above, alkyl impurities in the polysilane were decreased to less than 0.3% (from 1.4%), as determined by ¹H NMR spectroscopy (the chemical shift [or peaks] at 0.9 ppm and 1.3 ppm are assigned to alkyl impurity groups in the polysilane).

Example 1

Synthesis of Cp₂ZrPh₂ catalyst. Cp₂ZrCl₂ (10.18 g, 34.8 mmol) and 80 ml of DME were added to a 1 L Schlenk flask with a thermowell in the glove box. An addition funnel with 25 ml of 3M PhMgBr in ether was connected to the Schlenk flask. The setup was then connected to the Schlenk line. PhMgBr in ether was added slowly to a vigorously stirred solution maintained at a temperature of from 0 to 10° C. The reaction mixture was stirred overnight at room temperature after the addition. Thereafter, 80 ml of toluene was added to the reaction mixture and stirred for 30 minutes in the glove box. After removing the reaction residue by filtration, the dark green solution was dried under vacuum at 20° C. The resulting brown product was washed three times with 40 ml ether. 7.28 g of final product was obtained after drying overnight under vacuum (yield: 56%). The Cp₂ZrPh₂ catalyst was stored in an amber vial at −30° C. ¹H NMR (d₆-benzene): δ 7.35 (d, 4H), 7.20 (t, 4H), 7.12 (q, 2H), 5.77 (s, 10H). Elemental analysis, Calc: C 70.33%, H 5.37%, Zr 24.30%; Anal: C 68.83%, H 5.29%, Zr 23.12.

Example 2

Synthesis of polyphenylsilane. PhSiH₃ (22 g, 400 mmol) and Cp₂ZrPh₂ (0.381 g, 2 mmol) were mixed together in a Schlenk flask in the glove box. The reaction started immediately after mixing with the observation of H₂ gas evolution. The flask was then connected to Schlenk line within 10 min. The reaction mixture was stirred under argon flow for 5 days at room temperature. To remove the Zr catalyst, the yellow to brown polyphenylsilane as synthesized was dissolved in 120 ml toluene, washed 5 times with 3% HCl (150 ml acidic water, stirred for 20 min. in each wash) and once with 150 ml DI water (stirring for 20 min). The polyphenylsilane solution was then purified with chromatography using 60 g Florisil (Aldrich, 100-200 mesh) as the stationary phase and toluene as solvent. About 300 ml eluant was collected into a 500 ml flask. The toluene was removed at room temperature and the polyphenylsilane was further dried under vacuum at 80° C. for two hours to get 19.6 g clear or slightly yellow product (yield: 89%). ¹H NMR (d₆-benzene): δ 7.2 (bs, 5H), 5.1 (bs, 0.2H), 4.6 (bs, 0.8H).

FIG. 5 shows a GPC trace of a typical polyphenylsilane synthesized by this procedure. The polymer has a bimodal distribution. The lower molecular weight fraction contains a mixture of cyclic silanes with approximately five to six Si units. According to the number average molecular weight Mn as indicated in Table 1 below for the entire product distribution, the polyphenylsilane product mixture contains an average of about 10 to 12 Si units. Thus, the higher molecular weight fraction is believed to contain predominantly the desired linear polyphenylsilane and have an average of more than 10-12 Si units. Thus, n, b and/or q*m may be defined as an average number of silicon and/or germanium atoms in the polysilane (or the dehydrocoupling reaction product mixture), as calculated from the number average molecular weight (Mn) of the polysilane. The cyclic compounds are reasonably unavoidable byproducts, due to the mechanism of the catalyst and the stable nature of the cyclic compounds. The average yield of cyclic compound is about 20% as determined by ¹H NMR spectroscopy (the proton chemical shift of cyclic silane is around 5.1 ppm, and the linear polymer is around 4.6 ppm; see, e.g., FIG. 6A). Thus, the higher molecular weight fraction is believed to have an average of about 11 to 14 Si units.

TABLE 1 Molecular weight variation of linear polyphenylsilanes. Batch Mw Mn Linear %* 1 2370 1340 83 2 2280 1260 79 3 2880 1450 81 4 2094 1161 79 5 2310 1240 82 Mw: weight avg. molecular weight; Mn: number avg. molecular weight; *estimated from NMR spectra.

The above described polyphenylsilane purification procedure advantageously removes substantially all of the Zr catalyst. As shown in Table 2 below, the Zr content is about 0.23% if the polyphenylsilane is only washed with water. The amount is reduced to below 0.00001% with the combination of water washing and chromatography. Such reductions advantageously improve stability of a subsequently-produced polysilane.

The stability of polysilane was tested by exposing a 15% polysilane ink in cyclooctane under light at 50° C. A higher Zr content in the polyphenylsilane results in less stable polysilane inks. By removing substantially all of the Zr in the polyphenylsilane, the polysilane ink can survive more than 20 days at 50° C. in light. An ink of polysilanes synthesized from polyphenylsilane with a higher Zr content usually forms a white precipitate within three days under the same conditions.

TABLE 2 Stability of polysilanes. Zr % in Stability of Batch Polyphenylsilane workup polyphenylsilane polysilane, days 1 Water wash only   0.23      3 2 Water wash + chromatography <0.00001 >20 3 Water wash + chromatography   0.00005 >20 4 Water wash + chromatography <0.00001 >20 5 Water wash + chromatography <0.00001 >20

Example 3

Synthesis of polysilane. In a 500 ml Schlenk flask, 9 g of polyphenylsilane obtained as above described was dissolved with 100 ml of purified cyclohexane, and 0.25 g sublimed AlCl₃ was added to the solution. The flask was connected to a Schlenk line. The reaction mixture was frozen in liquid nitrogen and left under vacuum. The reaction mixture was thawed with a water bath while under static vacuum. Dry HCl gas was then backfilled into the reaction flask under vigorous stirring at room temperature. The solution was stirred 3 hours under continuous HCl flow. After stopping the HCl flow, the solution was stirred overnight under a static HCl atmosphere. The reaction solution was then connected to vacuum for about a minute to remove excess HCl.

36 ml 1M LAH solution (purified as described above) was added to the resulting polychlorosilane solution at 0 to −10° C. The addition was finished in about 30 min, and the reaction mixture was brought to room temperature and stirred overnight. Two phases were formed during this period. The top clear phase containing polysilane was decanted into another Schlenk flask, and was concentrated to about 10 ml by vacuum. The resulting polysilane cyclohexane solution was transferred to an amber vial containing 20 ml degassed DI water. The two phases were mixed vigorously, and allowed to set for 1 min. The top phase containing polysilane was transferred to another vial, and the same water wash procedure was repeated. After the second water wash, the polysilane phase was filtered through a 0.2 μm membrane to obtain a clear liquid which was dried under vacuum for 2 hours. 1.2 g of the final product was obtained as a slightly viscous clear liquid (yield 45%). ¹H NMR (d₆-benzene): δ 3.5 (bs, SiH) (see, e.g., FIG. 6C). ²⁹Si NMR (d₆-benzene): δ −96 (SiH₃), −106 (SiH₂), −128 (SiH).

Treating the polysilane mixture with water after reduction reduces the amount of Al in the polysilane, and substantially removes Al contamination in the Si film after spin coating. The treatment with water may also be carried out with slightly acidic water. Exposure of the silane mixture to alkaline conditions should be avoided as it may lead to uncontrolled Si—Si bond scission and polymerization. Contact with water can occur by either adding the polysilane mixture to water or adding the water to the polysilane mixture. The ratio of water to polysilane mixture is about 2:1. In most cases, washing the polysilane once is enough to remove most Al contamination. However, the reaction of Al residue with water may vary due to the nature of long chain polymer. Washing the polysilane at least twice with water ensures a consistent Al removal effect.

The polychlorosilane and polysilane are generally light and temperature sensitive. The ¹H NMR spectrum of an isolated polychlorosilane is shown in FIG. 6B. To avoid any unwanted isomerization or generation of higher molecular weight components, the reaction setup is preferable protected from light and UV, for example, using amber flask or wrapping with aluminum foil. The isolated neat polysilane is stored in amber vial at low temperature (−30° C.).

Example 5

In separate procedures, PhSiH₃ was dehydrocoupled using Cp₂ZrPh₂ and Cp₂ZrBu₂ catalysts (generated in situ by reacting Cp₂ZrCl₂ with, e.g., 2 mole equivalents of PhMgBr and BuLi, respectively) to yield a polyphenylsilane. The catalyst in the resulting polyphenylsilane was removed as described above. Cleavage of the phenyl groups and reduction of the product as described above yielded a polyhydrosilane, which was used in a viscous ink (e.g., about 10 wt. % in cyclooctane) for spincoating (with and without UV irradiation) and inkjet printing of silicon films.

Example 6

As shown in FIG. 3, cyclo-Si₅H₁₀ was dehydrocoupled using (Fl₂SiMe₂)ZrBu₂ catalyst (where Fl is fluorenyl), and the metal catalyst was removed by above described method to yield an oligohydrosilane, which was used in an ink (e.g., about 10 wt. % in cyclooctane) for UV-spincoating and inkjet printing of silicon films. The thus-produced oligohydrosilane exhibited beneficial effects in increasing the ink viscosity relative to similar compositions that did not include such an oligohydrosilane.

Example 7

Si Film Formation. The silane ink is formed by dissolving the polysilane in a compatible organic solvent, such as a mono- or multicyclic aliphatic hydrocarbon (e.g., cyclooctane and/or cis-decalin). The goal is to form a silane film or island from a polysilane ink by an ink jet printing technique. For effective ink jet printing, the ink should have a viscosity >3 cP (preferably about 10 cP) and low volatility. Inks from the present polysilanes meet these specifications. As shown in FIG. 7, the viscosity of the polysilane ink is above 4 cP when the mass loading is above 15% (either wt. % or vol. %), while the viscosity of a similar cyclopentasilane ink is just around 2 cp.

A silane film was formed by a spin-coating technique. About 0.4 ml of an ink containing ˜10 vol % polysilane in cyclooctane was dispensed onto a substrate in the glove box. A silane film was formed by spin-coating the ink onto the substrate with substantially simultaneous UV irradiation. The substrate with the silane film formed thereon was soft cured on a hotplate at 100° C. for about 10 min, then hard cured in a 400° C. oven under argon flow for 20 min. This procedure formed a hydrogenated, amorphous silicon film with a thickness of from 50 to 100 nm, depending on the spin-coating conditions and ink concentration. A typical SIMS profile of certain impurity atoms in the obtained film is shown in FIG. 8. The carbon, oxygen, hydrogen content in the film is about 0.08%, 0.03%,and 2.8%, respectively. Al is present in an amount of about 0.06 ppm. Both Fe and Na content are below the SIMS detection limit.

CONCLUSION/SUMMARY

As described above, poly- and oligo-hydrosilane and -hydrogermane compounds for semiconductor inks can be synthesized by dehydrocoupling of perhydrosilanes and perhydrogermanes (linear, branched, cyclo-, caged, poly-, or oligosilanes and/or -germanes), or by dehydrocoupling of arylhydrosilanes and arylhydrogermanes, followed by halogenative cleavage of the aryl groups and reduction to yield perhydrosilanes and perhydrogermanes. The inks can be used for production of amorphous and polycrystalline silicon, germanium, or silicon-germanium films by spincoating or inkjet printing, followed by curing at 400-500° C. and (optionally) laser-, heat-, or metal-induced crystallization (and/or dopant activation, when dopant is present; also see, e.g., U.S. Pat. No. 7,951,897, filed Oct. 11, 2005, filed concurrently herewith and incorporated herein by reference in its entirety). Highly doped films may be used to make contact layers in MOS capacitors, TFTs, diodes, etc. Lightly doped films may be used as semiconductor films in MOS capacitors, TFTs, diodes, etc.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

1. A method of forming a semiconductor film, comprising: coating or printing onto a substrate a composition that includes (i) a polysilane, a polygermane or a polysilagermane and (ii) a solvent in which the polysilane, polygermane or polysilagermane is soluble, wherein the polysilane, polygermane or polysilagermane consists essentially of blocks of —(AHR)—, —(—A_(k)H_(2k)—)— and/or -(cyclo-A_(m)H_(pm−2)R′_(rm)) units, where each instance of A is independently Si or Ge; each instance of R and R′ is independently H or halogen, k is an integer of from 2 to 12, p is 1 or 2; (p+r)=2; m is independently an integer from 3 to 12 for each block, and the polysilane, polygermane or polysilagermane has at least 10 A atoms; irradiating said composition with UV radiation, simultaneously with or immediately subsequent to coating or printing said composition onto said substrate; heating said coated or printed composition sufficiently to remove volatile components and form an amorphous, hydrogenated semiconductor film; and annealing and/or irradiating said amorphous, hydrogenated semiconductor film sufficiently to at least partially crystallize and reduce a hydrogen content of said amorphous, hydrogenated semiconductor film and form said semiconductor film.
 2. The method of claim 1, wherein said composition further comprises one or more dopants.
 3. The method of claim 1, wherein the solvent is selected from the group consisting of linear alkanes, cycloalkanes, polycycloalkanes, (cyclic) siloxanes and fluoroalkanes.
 4. The method of claim 3, wherein the solvent is a liquid at temperatures of 15 to 30° C.
 5. The method of claim 3, wherein the solvent is a (cyclic) siloxanes selected from siloxanes of the formula (R″₃Si)(OSiR″₂)_(p′)(OSiR″₃) and cyclosiloxanes of the formula (SiR″₂O)_(q′), where p′ is from 0 to 4, q′ is from 2 to 6, each R″ is independently H, C₁-C₆ alkyl, benzyl or phenyl substituted with from 0 to 3 C₁-C₄ alkyl groups.
 6. The method of claim 3, wherein the solvent is one or more C₃-C₈ fluoroalkanes substituted with from 1 to (2x+2) fluorine atoms, where x is the number of carbon atoms in the fluoroalkane.
 7. The method of claim 3, wherein the solvent is selected from the group consisting of C₆-C₁₂ monocycloalkanes and C₁₀-C₁₄ di- or tricycloalkanes.
 8. The method of claim 7, wherein the solvent is a C₆-C₁₀ cycloalkane.
 9. The method of claim 1, wherein said composition has a viscosity of about 2.5 to about 20 cP prior to coating or printing.
 10. The method of claim 1, wherein heating said coated or printed composition comprises soft curing said coated or printed composition at a temperature of ≦200° C.
 11. The method of claim 10, wherein the soft curing removes volatile components and further polymerizes said coated or printed composition.
 12. The method of claim 10, wherein heating said coated or printed composition comprises hard curing said coated or printed composition at a temperature of ≦600° C.
 13. The method of claim 1, wherein irradiating said amorphous, hydrogenated semiconductor comprises laser irradiation of said amorphous, hydrogenated semiconductor.
 14. The method of claim 1, further comprising doping said coated or printed composition by ion implantation, ion showering, or spin-on-dopant.
 15. The method of claim 2, wherein the one or more dopants comprise compounds of the formula D_(a)H_(b) and/or D_(a)R⁶ _(b′), where D is Sb, As, P or B; a is from 1 to 20; b is from 0 to 26; each of the b′ instances of R⁶ is independently H, alkyl, aryl, aralkyl or AR^(2′) ₃; where R^(2′) is hydrogen, alkyl, aryl, aralkyl or A_(y)H_(2y+1), and y is an integer in the range of 1 to 4; and b′ is an integer corresponding to the number of binding sites available on the “a” instances of D.
 16. The method of claim 2, wherein said composition further comprises one or more doped silane and/or germane compounds of the formula (R^(2′) ₃A)_(r′)A_(c)(DR⁶ ₂)_(s), where D, a, R^(2′), and R⁶ are as described for the one or more dopants; c is 1 to 4, r′+s=2c+2, and s≧1.
 17. The method of claim 1, wherein the substrate comprises a surface oxide layer.
 18. The method of claim 1, wherein the blocks of the polysilane, polygermane, or polygermasilanes have the formula —(—A_(k)H_(2k)—).
 19. The method of claim 18, wherein the polysilane, polygermane or polysilagermane has from 10 to 50 A atoms.
 20. The method of claim 1, wherein the polysilane, polygermane, or polysilagermane includes one or more blocks of the (cyclo-A_(m)H_(pm−2)R′_(rm))— units, where each instance of m is an integer from 5 to 8 for each unit.
 21. The method of claim 13, wherein annealing is conducted prior to irradiating said amorphous, hydrogenated semiconductor.
 22. A method of forming a semiconductor film, comprising: coating or printing onto a substrate a composition that includes (i) a polysilane, a polygermane or a polysilagermane and (ii) a solvent in which the polysilane, polygermane or polysilagermane is soluble, wherein the polysilane, polygermane or polysilagermane consists essentially of blocks of —(AHR)—, —(—A_(k)H_(2k)—)— and/or -(cyclo-A_(m)H_(pm−2)R′_(rm))— units, where each instance of A is independently Si or Ge; each instance of R and R′ is independently H or halogen, k is an integer of from 2 to 12, p is 1 or 2; (p+r)=2; m is independently an integer from 3 to 12 for each block, and the polysilane, polygermane or polysilagermane has at least 10 A atoms; irradiating said composition with UV radiation, simultaneously with or immediately subsequent to coating or printing said composition onto said substrate; and heating said coated or printed composition sufficiently to remove volatile components and form an amorphous, hydrogenated semiconductor film. 